RE: VW's VAQ 'diff' explained

[nickfrog]

scherzkeks said:

nickfrog said:

You're quite right Clivey. And that's the heart of the matter : it's the other important parameter but unlike the set up, it can't really be fiddled with as you know. Hence we end up with decent VAG cars that will always be compromised by having so much engine weight ahead of the front axle and therefore compromised polar moment of inertia (no wonder the R8 is the exception !!)

If you start with a balanced package through a good weight distribution you have an optimised package where all of the lateral grip can be distributed equally between front and rear and therefore can be totally used (and at which point, all of the adhesion potential can be used, leaving nothing for traction anyway before starting unwinding lock past the apex, which renders 4wd totally useless whereas the more dynamically compromised package will NEED 4wd to compensate for the inherent imbalance, but at least it helps the novice driver to manage traction).

Most road cars have compromised weight distribution and front-mount engines, so it is puzzling that you compare the finer points of the Golf's handling to that of a purpose-built, mid-engined sports car. We do agree that setup is of primary importance, but this is not something you seemed to find important in past discussions (if one could call them that).

In terms of the benefits of four driven wheels as related to cornering, aside from being able to put down more power on corner exit than a 2WD car (an obvious advantage in a performance context), and properly driven, an AWD car will lose lateral traction under power at a later point than a comparable 2WD vehicle, as it does not push all power to a single axle, but distributes it over 4 contact patches. Pretty basic, but perhaps was not covered in your copy of the Driving God FAQ -- which also apparently does not approve of HPDE instruction, or worthwhile publications from Milliken, etc. You know, stuff people who've been driving for some 30 years would have sought out out at some point.

But you're the guy who, by your own admission, is still using a track instructor (after 30 years of driving ?) and ridiculed himself in past threads (here : http://www.pistonheads.com/gassing/topic.asp?h=0&a... )trying to tell seasoned track drivers how to drive and that effectively you can drive totally neutrally on the limit (or is that at 6/10ths?), when even F1 drivers can't.

I haven't compared a Golf to an R8. Ever heard of front mid-engine ? Can't you comprehend that front engineds road cars have varying degrees of compromise : just look at how much of the engine in a VAG car is ahead of the front axle (most of it). Now open the bonnet of a BMWs : most of the engine is behind the front axle. Do you understand that fundamental (and that really is not an exaggerated adjective) difference and the dynamic implications ? Do you understand the impact that the lower polar moment of inertia will have in the car's ability to change direction ? Can't you also understand how even a slightly lower COG can have a significant impact on lat grip ? Can't you understand that a 50/50 weight balance (for all the marketing BS ;-)) will actually mean that the chassis will inherently work its front and rear tyres with equal load even off the throttle ? AFAIK, VAG cars are still nowhere near 50/50 when BMW cars are. But on the other hand, they have more interior space, so it's not all bad for family duties. We're looking at very very basic car dynamics concepts worthy of a 1st month in engineering not some outlandish theories or complicated kinematics (talking of which though when did you last look at the degree of sophistication of the rear suspension arrangement of a basic 1-series compared to an A3's ?)

scherzkeks said:

lose lateral traction under power

That's a brutal contradiction in terms that proves that you still don't understand the notion of traction circle nor therefore the difference between lateral grip and longitudinal acceleration nor their relationship, which is a worry for someone who has been driving for 30 years

scherzkeks said:

aside from being able to put down more power on corner exit than a 2WD car (an obvious advantage in a performance context)

A 4WD car CAN'T put any more power than a 2WD car when all of the adhesion potential is used up by lateral grip and that there is NONE left for traction : and in a performance context you're always going to use all of the lat grip, aren't you ? Or maybe you won't, hence my long held assumption that you scare yourself at 6/10ths which is why you can ALSO use some traction, not because 4wd adds any, but because you're not using all the adhesion hence your view that 4wd adds grip and neutralises a car. It doesn't. It just makes traction management easier : geddit ? Again, we're down to that poor old traction circle that you do not comprehend. But don't take my word for it :

Max_Torque said:

And the following statement is CRITICAL:

"A tyre can supply a maximum force vector at its contact patch for any given vertical load. That vector is the summation of the Lateral and Longitudinal forces acting on that tyre"

What that means is that increasing one component of the total force vector, say the lateral load, MUST necessarily reduce the other component of that vector so as not to exceed the magnitude of the total force vector available.

READ THE SENTENCE IN BOLD AD NAUSEAM OR UNTIL YOU GET IT AND THEN REPORT BACK

You have developed a tendency to project your own shortcomings on other people when there should be no shame in starting your track career (at any age), we all have to start somewhere. I know you are quite good with books and internet research and HDPE but don't forget one element : many here have been involved in motorsport and racing for quite a long time, and not just with the theory so when you repeatedly try to teach granny how to suck eggs eventually someone gets annoyed (not me, it just makes me smile).

Instead, why don't you come and show us what you can do ? Ring on 02/03/04 October. It's a friendly invitation, I am always happy to learn tips and share experiences with fellow track enthusiasts, one of us is an ex LMP2 driver so maybe there will be someone of your talent. Surely if I can make the effort from the UK, a few miles shouldn't be difficult for you ?

Edited by nickfrog on Sunday 17th August 19:48

[Byronwww]

This thread seemed to go a bit weird, I have one of these on my wrong wheel drive car.
Not a driving god and I've only got an open diff RWD car, an Evo rally car with mechanical diffs (which felt insane doing their thing before the man stopped me having fun) to compare to.


There normally isn't enough visibility on road to get it noticeably kicking in but on a cold wet day I was messing about on small roundabouts and figured it out. On fast roundabout exits you really have to be planting it beyond where I'd expect to understeer straight off, there's a split second feel of hesitation and then it just tucks in and pulls you into the line you are steering towards.

The different drive modes also set how aggressively it kicks in, in cupra mode on the small slippery roundabouts it felt really aggressive and I almost got caught out getting tugged towards the inside pavement.